Add [EE] tag but I do not know anything about tubes. On Tue, May 12, 2009 at 10:11 AM, Richard Prosser wro= te: > =A0Brusque > > Have you tried the "listen" test to a virgin tube? As I recall, most > tubes would have elements that would vibrate when shaken. Mostly the > various grids etc although the whole structure can also vibrate/rattle > a bit. > > Is it causing a problem? Are you getting excessive microphony / feed back= etc? > > Since the grids etc. are sitting in a vacuum they will not be subject > to speaker vibration directly, can you mount the valves using a > damping material or clamp them to something solid? > > I don''t thing any external magnetic field from a speaker would be > enough to cause a problem. (I have seen how a magnetic field from a > power transformer can effect a CRT tube however - took a while to > figure out why part of the trace was running "backwards"). > > RP > > 2009/5/12 Edson Brusque : >> Hello, >> >> =A0 =A0 I have a question that maybe some of the tube guys on the list c= an >> answer. >> >> =A0 =A0 Can a speaker's magnetic field interfere with tubes/valves and >> damage it? >> >> =A0 =A0 Let me try to explain the situation. I've made some combo guitar >> amps. They are just prototypes I'm making while studying tube circuits. >> They uses a pair of 6L6 in the power section and gives close to 40W >> maximum output power. >> >> =A0 =A0 Almost all the 6L6s (3 pairs) I've been using have developed tub= le >> rattle. I still have to make a simple single ended power amp to >> individually test the tubes and discover wich ones are really >> compromised but it seens all 6 have different levels of rattle. Tapping >> the tubes with a finger while holding it near the ear, I can hear >> something vibrating inside the tubes. The frequency/volume of the >> vibrations changes from tube to tube and also depending on where I tap. >> >> =A0 =A0 This is really intrigging me. The power section works at about 4= 50V >> on the tubes plates. Plate current is about 45mA (each tube). Screen >> grid voltage is about 420V and current is bellow 2mA. The power >> dissipation seens to be well bellow the maximum allowed. I don't have >> any fan blowing air to keep the tubes cool, but there's some airflow by >> convection. >> >> =A0 =A0 Now, one the power tubes are very near one of the speakers (it's >> two 10 inches). The physical layout, side-looking, is something like: >> >> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 . >> =A0 =A0+--+ =A0+--+ =A0 =A0 =A0/| >> =A0 =A0|V1| =A0|V2| =A0 =A0 / | >> =A0 =A0| =A0| =A0| =A0| .--| =A0| >> =A0 =A0'--' =A0'--' | =A0| =A0| >> =A0 =A0 =A0 =A0 =A0 =A0 =A0 '--| =A0| >> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 \ | >> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0\| >> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 ' >> >> =A0 =A0 I've been looking for a mail group about audio tubes/valves >> circuits but haven't found anything interesting. Maybe there's a >> "tubelist" somewhere? >> >> =A0 =A0 Best regards, >> >> =A0 =A0 Brusque >> >> >> >> -- >> --------------------------------------------------------------------- >> Edson Brusque =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0Stagetronics Eletro= Eletr=F4nicos Ltda >> Research and Development =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 Blumenau = =A0- =A0SC =A0- =A0Brazil >> http://www.ryan.com.br/netiqueta.htm =A0 =A0 =A0 =A0 =A0 =A0 www.citroni= cs.com.br >> --------------------------------------------------------------------- -- = http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist